These threads about..."if you could only have one" are about the silliest exercises I know of.
And then writes a book about it.....
The OP is a good start...
Just needs some photos and another chapter or two...
Just one gun (man, writing that gives me heartburn), it would be hard to beat the vanilla '06. You can load it to do just about anything, although maybe not spectacular, very middle of the road and serviceable.
DF